1. Field of the Invention
The present invention relates to a washing machine or laundry machine equipped with an optical sensor for detecting the light permeability of a detergent or rinse water in a washer tank.
2. Description of the Prior Art
A washing machine of the type referred to above, namely, a washing machine equipped with an optical sensor for detecting the light permeability of a solution of washing detergent, i.e., for detecting the amount of light that can penetrate the detergent solution, has been disclosed in Japanese Patent Laid-open Publication No. 61-50595. More specifically, the washing machine of Tokkaisho 61-50595 is provided with an optical sensor comprised of light emitting and light receiving elements confronting each other in a washer tank, whereby the light permeability of the detergent solution in the washer tank is detected using an output of the light receiving element. A control circuit to which is generated an output of the sensor obtains data depicting the dirt contents of the laundries on the basis of the time period consumed from the start of washing until the light permeability detected by the optical sensor decreases to a predetermined value (20% of the light permeability of clear water), and the washing machine is operated according to the dirt content data of the control circuit.
Meanwhile, a washing machine disclosed in Japanese Patent Laid-open Publication No. 61-159999 has been devised taking note of the fact that the light permeability detected by the optical sensor gradually increases after the start of washing, and thereafter it gradually decreases. A time point at the interface between the increase and decrease of the light permeability is set as an initial value of the data. In this washing machine, the type of detergent and the like are detected on the basis of both the time spent before the light permeability reaches the interface after the start of washing, and the changing width of the light permeability.
In the washing machine disclosed in Japanese Patent Laid-open Publication NO. 61-50595, however, if the light emitting surface of the light emitting element or the light receiving surface of the light receiving element is stained, the light intensity coming from the light emitting element to the light receiving element lessens thereby diminish an output from the light receiving element. Accordingly, the light permeability detected by the optical sensor is a lower value than the actual value of the light permeability of the detergent in the washer tank. In consequence, the light permeability detected by the optical sensor reaches the predetermined value after the start of washing more quickly in comparison to the case where the elements are not stained. Therefore, the dirt content is erroneously detected. Particularly, since during use of the washing machine laundries and detergent are put in the washer tank, the light emitting and receiving elements provided in the washer tank are unavoidably stained. Moreover, the amount of the stain is generally increased in proportion to the usage time of the washing machine. As a result, the detecting accuracy of the optical sensor deteriorates with time. Accordingly, the optical sensor cannot be relied upon for a long service in the detection of the dirt content of laundries.
Meanwhile, the change in the light permeability of the detergent solution in the washer tank is greatly influenced by the type of the detergent being used. Liquid detergent changes the light permeability significantly less than powdery detergent, and the light permeability of liquid detergent may not be reduced to 20% of that of clear water. In such case, it is impossible to obtain the dirt content data. Therefore, the washing machine disclosed in Tokkaisho 61-50595 is not able to control washing operation in a manner which is responsive to the type of the detergent being used.
On the other hand, the washing machine disclosed in Tokkaisho 61-159999 is designed to detect the type of cleanser. However, according to the disclosed detecting method the type of the detergent can be detected only when the detergent is supplied into the tank before the water is added at the start of washing. In other words, if the detergent is put into the tank after the start of washing (after the start of stirring), the light permeability detected by the optical sensor declines after the start of washing. However, since the washing machine is arranged to operate based on the notion that the light permeability detected by the optical sensor increases at the start of washing and then, gradually decreases, the washing machine cannot detect the type of the detergent if the detergent is put into the tank after the start of washing. In addition, the change in the light permeability of the optical sensor is dependent not only on the type of detergent, but is also dependent on the amount of the detergent, and accordingly the light permeability detected by the optical sensor does not always follow a constant pattern of increasing once after the start of washing and thereafter decreasing.